Pulling apparatus

ABSTRACT

An apparatus for pulling retrievable subsurface devices mounted internally of a tubular string. The apparatus includes a hydraulic motor and a latching assembly. The apparatus is lowered through the tubular string bringing the latching assembly into gripping engagement with the retrievable device. Actuation of the hydraulic motor imparts an upward pulling force on the device which tends to dislodge the device from its seat.

United States Patent Inventor Jafkm Kennel 2,984,302 5/1961 Church 166/98 gl z gfl 3,016,954 1/1962 Crowell 166/98 2] A 1. N0. 31 3 fif 9, 1969 Primary Examiner-James A. Leppmk i [45] Patented Jam 19 1971 Attorneys-James A. Reilly, John B. Davidson, Lew1s H. [73] Assignee E580 Production Research Company Eatherton, James E. G1lchr1st, James E. Reed and Robert L.

a corporation of Delaware Graham [54] PULLING APPARATUS 14 Claims, 2 Drawing Figs.

[52] US. Cl 166/98,

294/361 ABSTRACT: An apparatus for pulling retrievable subsurface [5 1] Int. Cl E21! 31/00 d i n d internally of a tubular string. The apparatus Fleld Search 6 includes a hydraulic motor and a latching assembly. The apparatus is lowered through the tubular string bringing the latching assembly into gripping engagement with the retrieva- [56] References cued ble device. Actuation of the hydraulic motor imparts an up- UNlTED STATES PATENTS ward pulling force on the device which tends to dislodge the 2,377,249 5/1945 Lawrence 166/98 device from its seat.

1 i ll 1 s 1 it Q 50 l *k IO 1 I a I;

1 I [4| 49 GI t 23 1 4a 1 l 62 l 42- 1 1 42 53 v 52 1 1 411 1 2 l as '25 '58 5 5 -37 34 l FIG. 2

INVENTOR. JACKSON M, KELLNER ATTORNEY PAIENTEDJAN 19 I971 FIG. I

8 4 mm a RIU 2 L M 5 ML Ill 6n 1\Y@\\V/ m M l %A////////VV////////A/?//// J W l m 4 5 2 4/ E 0/ 4 2 5 6 5 PULLING APPARATUS BACKGROUNDAND SUMMARY or THE INVENTION This invention relates to retrievable subsurface equipment. in one aspect it relates to a pulling apparatus for retrieving subsurface devices detachably mounted in tubular strings. In another aspect it relates to retrievable drilling bits. I

The use of retrievable devices in well drilling, completion, and production operations offers convenient and inexpensive means for controlling subsurface conditions. ln-practice, the device, such as a flow choke, safety valve, gas lift valve, drilling bit insert, etc.,is lowered through the tubular string to a seating surface located at a predetermined depth in the tubular string. Once located, the device performs its assigned function. A particular feature of such a deviceis its retrievability by mobile surface equipment such as wireline equipment. Frequently, however, because of corrosion and sanding up, the force required to dislodge the device exceeds the pulling capacity of conventional wireline equipment. If the design permits, the device can bedislodged by reverse circulation techniques. However, this technique is not recommended because of the attendant hazard of fracturing the exposed for mation which could result in lost circulation. 1

The present invention provides for a pulling apparatus operative to exert a pulling force on a retrievable device inde pendent of wireline strain and reverse circulation techniques. The apparatus includes a latching assembly adapted to grip the retrievable device and a hydraulic motor operatively responsive to the pressure in the tubular string. Briefly, the apparatus is lowered through the tubular string until the latching assembly grippinglyengages the retrievable device. The pressure in the string is then increased causingthe motor'to impart an upward pulling force on the device." I

As indicated above, the pulling apparatus constructedac cording to this invention can be used-to retrieve a variety of devices detachably mounted in a tubular string. This invention finds particular application in retrieving drilling bit inserts which because of the severe operating conditions are extremely difficult to dislodge from their associated seating surface. Accordingly, this invention will be described in connection with jet drilling bits, it being understood that the principles examplified thereby are equally applicable to other applications such as those listed above.

Jet nozzles have long been used in conventional rock bits and serve to direct a high velocity stream which effectively cleans the bit cones and carries cuttings away from the bit. More recently, jet streams have been used as the principal medium for 'drilling wells. It has been found that power transmitted to the rock by high velocity jet streams is sufficient to shatter the rock thereby forming the wellbore.

. In hydraulic jet drilling, the bits must be provided with a relatively small nozzle or orifice which in relation to the pressure differential thereacross develops extremely high velocity streams. The power transmitted by the jet stream causes the rock to shatter into fragments which are carried to the surface by the liquid returning through the annulus. As might be expected, the high velocity jet stream presents severe erosion problems on the bit. Notwithstanding the construction of the bits of hard material such as tungsten carbide, the nozzle becomes severely eroded in a relativelyshort period of time. Erosion increases the effective flow area of the nozzles and causes a decrease in the differential pressure thereacross, the efi'ect of which is to reduce the stream velocity and hence its drilling capacity thereof. 7

The conventional technique for replacing a worn drilling bit involves a sequence of events known as a round trip which comprises pulling the drill string, replacing the bit, and rerunning the string. For deep wells round trips comprise a substantial portion of the rig time. For obvious economic reasons, it is desirable to reduce the round trip time to minimum. Retrievable nozzle holders adapted to be received in a bit body attached to the drill string have been proposed. Heretofore, the retrievability of the holders depended primarily upon the pulling capacity of the wireline retrievers and/or upon forces developed by reverse circulation. Frequently, however, owing to wedging, sanding up, or. corrosion effects, extreme forces are required to dislodge the holder from the bit body. In these situations, the wireline equipment frequently is not capable of retrieving the holder, Furthermore, reverse cir culation is undesirable because of the attendant hazard of lost circulation.

The drilling bit and associated pulling apparatus contemplated by the present invention comprises a bit body adapted to be secured to the bottom of a tubular drilling string, a nozzle holder insertably, mounted in the bit body and detachable therefrom, and an apparatus for pulling the nozzle holder from the bit body. In operation the pulling apparatus is lowered through the drilling string and supportingly received in the bit body immediately above the nozzle holder. The device includes a hydraulic motor having a latching assembly which audevice dislodged from its seat and DESCRIPTION OF THE DRAWINGS.

,FIG. 1 is a cross-sectional view illustrating the relative positions'of the pulling apparatus and a subsurface retrievable device prior to the formerlatching onto the latter; and FIG. 2 is a view similar to FIG. .1 showing the retrievable suspended on the pulling apparatus.

' DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to the drawings, a hydraulic jet bit 10 is seen to include a body 12 and a generally cylindrical insert member which in this embodiment is in theform of a nozzle holder 13.

The bit 10 is threadedly connected to a tubular drilling string 11 and as illustrated is disposed at the bottom of a borehole 15. The bit body 12 has formed therein an internal opening 14 which is in fluid communication with the interior of the drilling string 11. The opening 14 includes an axially extending portion l6 and a diverging portion 17 which terminates at a lower open end 18 in the shape of an ellipse. The internal wall of bit body 12 which defines the diverging portion 17 is configurated to provide a beveled surface 19 for seating the retrieving device described below. The diverging portion 17 of opening 16 includes an upper circular section 20 and a lower circular section 21 of reduced diameter. The lower rim of section 21 is bordered by a shoulder 23 which serves to seat the nozzle holder 13. Attached to section 20 and lying in a vertical plane which passes through the major axis of elliptical opening 18 is a key 24. As described in detail below, the key 24 serves to properly orient the nozzle holder 13 in the bit body 12.

The nozzle holder 13 includes a hollow cylindrical body 25 open at the top and closed at the bottom by plug 26. The plug 26 has a cylindrical portion 27, the diameter of which is sized to provide a close tolerance fit in circular section 21. An extension 28 integrally formed with portion 27 projects downwardly therefrom. Beveled shoulder 29 is milled in extension 28 and is configurated to seat on surface 23 of bit body 12. The extension 28 is truncated to provide an elliptical surface 30 which with the holder 13 seated on beveled surface 23 lies flush with the bottom of the bit body 12 as shown in FIG. 1. Neoprene O-rings 31 mounted in suitable circumferentially extending grooves provide a fluid seall'at the bottom of the bit 10. A plurality of nozzles, two shown as 32, are formed in the plug 26. The number, size, and geometric location of the nozzles 32 will depend upon several factors including the type of drilling fluid used, pressure requirements, size of borehole, etc. While the nozzles 32 are shown cast in the plug 26, it should be realized that nozzle inserts can also be used in a manner well known in the art.

Since the longitudinal axis of the diverging portion 17 extends obliquely with respect to the longitudinal axis of the must be seated on body 12 under controlled conditions so that the major axis of the surface 30 aligns with the major axis of the complimentary-shaped opening 18. Accordingly, the nozzle body 25 has milled therein a pair of symmetrically and generally spirally extending guides or cams, one shown as 33 in FIG. 1. The cams 33 join at tip 34 near the lower end of nozzle body 25. Tip 34 lies in a vertical plane which passes through the major axis of elliptical surface 30. The upper ends of cams 33 terminate in axially extending straight portions 35 and are separated by space sufficient to receive key 24. Thus it is seen that the nozzle body 25 includes a full-diameter upper section and a lower section of reduced diameter. The outside diameter of the upper section is slightly less than the diameter of the bit body section whereas the diameter of the reduced lower section of nozzle body is substantially equal to the diameter of plug 26. A guide 36 secured to the body 25 on a milled-away portion and positioned generally in line with the keyway, defined by guide portions 35, 3S, maintains the nozzle holder 13 generally in axial alignment in passing through diverging portion 17. Secured to the geometric center of the top surface of plug 26 is an upwardly extending spear head 37.

ln positioning the bit 10 at the bottom of the hole 15, the nozzle 13 is pumped down the drill string 11. The nozzle holder 13 passes through the straight portion 16 and enters the diverging portion 17. In passing through the diverging portion 17 one of the cams 33 engages the key 24 so that further downward movement turns the nozzle holder 13 into proper alignment with opening 18. When the nozzle holder 13 has reached the position wherein the keyway, defined by guide portions 35, 35 is in registry with key 24, surface and opening 18 are in. proper alignment so that further downward movement seats the nozzle holder 13 on surface 23.

With the nozzle holder 13 properly positioned, the drilling operation is ready to begin. High-pressure fluid is pumped by surface facilities down the drill string 11 through the opening '14.and finally through the nozzles 32. The pressure dif ferential across the nozzles 32 is sufficiently large to create high-velocity streams jetting from the nozzle outlets. The high kinetic energy of the jet streams is spent on the rock formation causing it to shatter into fragments. The fluid in returning to the surface through the annulus carries the fragments away from the bit 10. The high pressure differential across the bit, which reaches as high as 15,000 p.s.i., has the effect of press fitting the nozzle holder 13 in the bit body 12. Furthermore, sand and other debris tends to collect in the annulus separating the holder body 25 and section 20. Consequently, the force required to dislodge the nozzle holder 13 from the bit body 12 is quite large, sometimes exceeding the pulling capacity of conventional wireline equipment. In hydraulic jet bits wherein the longitudinal axis of the holder 13 is disposed obliquely with respect to the longitudinal axis of the drill string 11, additional forces are required. The misalignment of the longitudinal axis of the nozzle holder 13 and the direction of the pulling force afforded by wireline equipment reduces the effective force operative to dislodge the holder 13. Furthermore, the misalignment tends to impart a turning moment on the nozzle holder 13 which could cause it to hang up in the areas of close tolerance.

The present invention provides a pulling apparatus 41 operative upon retrievable nozzle holders in such a manner that the pulling force is applied thereon independent of wireline equipment. As best seen in FIG. 1, the pulling apparatus 41 includes a support member 42 circular in cross section, a hydraulic motor 43 mounted on the support member 42, and a latching assembly 44 operatively connected to the hydraulic motor 43. The support member 42 is a disclike structure having a lower beveled edge 46 which is sized to seat on shoulder 19 formed in hit body 12. A neoprene O-ring 47 mounted in a circumferential groove formed in beveled edge 46 provides a fluid seal in the opening 14. The hydraulic motor 43 is a positive displacement type having a housing 48 defining an internal cylindrical chamber 49 and a piston 51 slidably mounted in chamber 49. A piston rod 52 connected to the piston 51 extends through the support member 42 and projects downwardly therebelow; The upper end of housing 48 is connected to a wireline 50.

The latching assembly 44, connected to the lower end of rod 52, is in the form ofa spear head overshot having a hollow body 53 which houses a pair of spring-loaded latching jaws 54 and 55. The latching jaws 54 and 55 are pivotally mounted on pin 56 secured to the body 53. The lower end of the jaws 54 and 55 have formed therein inwardly turned latch dogs 57 and 58, respectively, which are urged toward one another by latch spring 59. As the pulling apparatus 41 is lowered to the bottom of the hole 15, the overshot 44 passes over the spear head 37 forcing the jaws 54 and 55 outwardly against the bias of spring 59. When the dogs 57 and 58 clear the head 37, the spring 59 snaps the jaws 54 and 55 into gripping relation on the spear head 37. The equipment is designed so that the overshot 44 attains a grip on the spear head 37 just prior to 'the seating of support member 42 on surface 19.

The piston 51 is slidably mounted in chamber 49*from a lower position shown in H0. 1 to an upper position shown in FIG. 2. The piston 51 divides the chamber into an upper compartment 61 and a lower compartment 62. Port 63 formed in housing 48 provides fluid communication between the bit opening 14 and the lower chamber 62 so that the pressure internally of the bit body 12 is transmitted to the lower surface of piston 51. A shear pin 64 mounted in a suitable aperture provided in rod 52 engages the bottom of support member 42 thereby preventing operation of the motor 43 until the overshot 44 has attached to the nozzle holder 13. in this embodiment, the upper compartment 61 is sealingly charged with atmospheric pressure with piston 51 in the lower position (FIG. 1). In deep wells, it may be desirable to precharge compartment 61 with a predetermined pressure in order to control the differential pressure across piston 51. Thus a pressure differential across piston 51 tends to drive the piston 51 and equipment depending therefrom upwardly. In order to preclude movement of piston 51 and associated equipment until the overshot 44 has attached to the nozzle holder 13, the pin 64 is inserted through rod 52 prior to running the tool.

In operation let it be assumed that the nozzles 32 in nozzle holder 13 have become badly eroded and requires replacement. The pulling apparatus 41 with pin 64 properly inserted in rod 52 is lowered through the drill string 11 on the wireline 50. Upon approaching the seating surface 19, the overshot 44 is guidingly moved into generally axial alignment with spear head 37 Continued downward movement of the pulling apparatus 41 forces the jaws 54 and 55 outwardly around head 37 compressing the spring 59. Now when the latching dogs 57 and 58 clear the head 37, the bias of spring 59 causes jaws 54 and 55 to snap inwardly attaining a positive grip on head 37 At this point, the support member 42 has seated on shoulder 19 placing the pulling apparatus 41 in position for pulling the nozzle holder 13. When the member 42 is seated and pressure is applied in the column thereabove by actuation of surface pumps, liquid flowing through port 63 creates an upward force on piston 51. At a predetermined pressure, the pin 64 shears causing an upward jarring force to be applied to the nozzle holder 13. Note that the pressure differential across piston 51 is created by the hydrostatic pressure in the column above member 42 as well as by the pump pressure. increased pump pressure proportionately increases the pulling force imparted by the hydraulic motor 43. If the initial jarring action of the hydraulic motor 43 does not dislodge the nozzle holder 13 from the bit body 12, the pressure applied by the surface pumps can be relieved and repressured. It should be observed that because of the geometric arrangement of the pulling apparatus 41 in relation to the opening 17, the effective pulling force is the same as the applied pulling force.

Once dislodged from the bit body 12, the nozzle holder 13, suspended on overshot 4,4, is retrieved by pulling the apparatus 41 on the wireline 50. Alternatively, the apparatus can be provided with sealing tins'so that the retrieving operation can be accomplished by drilling fluidcirculation techniques. That is, the apparatus 41 is pumped down the string to engage and dislodge the retrievable subsurface device, and is pumped to the surface by reverse circulation.

Thus it has been demonstrated that the apparatus constructed according to this invention is capable of developing pulling forces on a nozzle holder independent of the wireline equipment and without resort to reverse circulation techniques. While this preferred embodiment has been described in particular detail, it should'be' understood that variations and modifications can be made therein without departing from the scope and spirit of the invention as set forth in the appended claims.

, .I claim:

1. An apparatus for pulling retrievable subsurface devices mounted internally of a tubular string, said apparatus comprising: a hydraulic motor passable internally through said tubular string; means for sealingly supporting said hydraulic motor in said tubular string at an elevation above said retrievable device; a latchingassembly depending downwardly from said hydraulic motor and including means for gripping said retrievable device with said hydraulic motor supported in said tubular string; said assembly being upwardly movable responsive to actuation of said hydraulic motor; and said motor being actuably responsive to pressure above said support means.

2. The invention asrecited in claim 1 wherein said hydraulic motor is a positive displacement motor having a housing defining an internal chamber, a piston reciprocable in said chamber, and a rod connected to said latching assembly, said chamber below said'piston being in pressure communication with theinterior of said tubing whereby the upward pulling force developed by said motor and imparted on said retrievable device is proportional tothe pressure in said tubing above said support means. i i

3. The invention as recited in claim2 and further comprising means for maintaining said hydraulic motor inoperative until said motor is sealingly supported in said tubular string.

4. An apparatus for drilling wells comprising: a hollow bit body attachable to the bottom of a tubular drilling string; said bit body and said drilling string being aligned for conducting a drilling fluid therethrough; an insert member detachably mounted in said bit body; said member being passable internally through said drilling string; a motor passable internally through said drilling string and insertable in said bit body; said body providing a support for said motor at'an elevation above said insert member; a latching assembly suspended from said motor and being upwardly movable responsive to-actuation thereof; said assembly including latching means for attachment to said insert member; and means foractuating said motor with said latching assembly attached to said member whereby an upward pulling force is exerted on said insert member. l i

5. The invention as recited in claim 4 wherein said motor is a positive displacement piston-actuated motor actuably responsive to the pressure of said drilling fluid above said support.

6. The invention as recited in claim 5 wherein said pistonactuated motor includes a housing defining a cylindrical chamber therein, means for pressure sealing said housing on said support, a piston reciprocably mounted in said chamber dividing said chamber into upper and lower compartments, and a piston rod connected to said piston, and extending downwardly through said housing, said piston rod having its lower end connected to said latching assembly, said lower compartment being in pressure communication with said drilling fluid above said sealing support sothat the pressure of said drilling fluid tends to drive said piston upwardly thereby applying a pulling force on said insert through said latching assembly.

7. In a jet drilling assembly having a hollow bit body attachable to the bottom of a tubular drillstring and a retrievable nozzle holder detachably mounted in said bit body, the improvement comprising a pulling apparatus adapted to be lowered through said drill string and including a hydraulic mo tor; a latching assembly depending from said hydraulic motor for attachment to said nozzle holder; and means for sealingly supporting said hydraulic motor in said drill string at an elevation above said nozzle holder, said latching assembly being upwardly movable responsive to actuation of said hydraulic motor, and said motor being actuably responsive to pressure above said support means.

8. The invention as recited in claim 7 wherein said bit body has formed therein an internal opening including a generally axially extending portion and a diverging portion, said diverging portion being formed to receive said nozzle holder and sealingly support said nozzle holder in a fixed attitude, said opening being contigu rated to provide a seat for sealingly supporting said pulling device at an elevation above said nozzle holder, and said motor is a positive displacement piston hydraulic motor operatively responsive to the pressure inter nally of said bit above 'said seat.

9. The invention as recited in claim 81 wherein said seat for supporting said pulling device extends circumferentially around said diverging portion and is configurated to support said pulling device in an attitude in which the direction of force applied to said nozzle holder is' coincident to the direction of movement of said nozzle holder through said diverging portion.

10. An apparatus for drilling wells, said apparatuscomprising: a tubular drilling string; a drilling but including a bit body connected to the bottom of said drilling string and having a longitudinal opening formed therein, said opening being in registry with the internal opening in said drilling string whereby drilling fluid is conducted from the surface internally through said drilling string and said bit, a generally cylindrical nozzle holder passable internally through said drilling string and insertable into said body opening, said bit body being provided with a seat for fixedly and sealingly receiving said nozzle holder; a hydraulic motor passable internally through said drilling string and insertable into said bit body opening, said bit body being provided with a seat for sealingly receiving said hydraulic motor at an elevation above said nozzle holder; latching means depending from said hydraulic motor for attachment to said nozzle holder, saidlatching means being upwardly movable responsive-to actuation of said hydraulic motor, said hydraulic motor being actuated by drilling fluid pressure above said hydraulic motor seat; and means for preventing actuation of said hydraulic motor until said hydraulic motor is positioned on said motor seat.

11. The invention as recited in claim 10 wherein said hydraulic motor includes a support member having a shoulder for sealingly engaging said motor seat, a housing extending upwardly from said support member and having a cylindrical chamber formed therein, a piston reciprocably mounted in said chamber dividing said chamber into upper and lower compartments, and a piston rod extending downwardly through said support member and having its lower end connected to said latching means, said housing having a port intercommunicating said lower compartment and said bit body opening whereby the upward force developed by said hydraulic motor is proportional to the drilling fluid pressure in said the internal, opening of said drill string and a lower diverging portion, said hydraulic motor seat being formed in said bit body in an upper portion of said diverging portion and said from said seat are in general alignment.

14. The invention as recited in claim 13 wherein said bit body includes means for orienting the attitude at which said nozzle holder engages said nozzle holder seat. 

1. An apparatus for pulling retrievable subsurface devices mounted internally of a tubular string, said apparatus comprising: a hydraulic motor passable internally through said tubular string; means for sealingly supporting said hydraulic motor in said tubular string at an elevation above said retrievable device; a latching assembly depending downwardly from said hydraulic motor and including means for gripping said retrievable device with said hydraulic motor supported in said tubular string; said assembly being upwardly movable responsive to actuation of said hydraulic motor; and said motor being actuably responsive to pressure above said support means.
 2. The invention as recited in claim 1 wherein said hydraulic motor is a positive displacement motor having a housing defining an internal chamber, a piston reciprocable in said chamber, and a rod connected to said latching assembly, said chAmber below said piston being in pressure communication with the interior of said tubing whereby the upward pulling force developed by said motor and imparted on said retrievable device is proportional to the pressure in said tubing above said support means.
 3. The invention as recited in claim 2 and further comprising means for maintaining said hydraulic motor inoperative until said motor is sealingly supported in said tubular string.
 4. An apparatus for drilling wells comprising: a hollow bit body attachable to the bottom of a tubular drilling string; said bit body and said drilling string being aligned for conducting a drilling fluid therethrough; an insert member detachably mounted in said bit body; said member being passable internally through said drilling string; a motor passable internally through said drilling string and insertable in said bit body; said body providing a support for said motor at an elevation above said insert member; a latching assembly suspended from said motor and being upwardly movable responsive to actuation thereof; said assembly including latching means for attachment to said insert member; and means for actuating said motor with said latching assembly attached to said member whereby an upward pulling force is exerted on said insert member.
 5. The invention as recited in claim 4 wherein said motor is a positive displacement piston-actuated motor actuably responsive to the pressure of said drilling fluid above said support.
 6. The invention as recited in claim 5 wherein said piston-actuated motor includes a housing defining a cylindrical chamber therein, means for pressure sealing said housing on said support, a piston reciprocably mounted in said chamber dividing said chamber into upper and lower compartments, and a piston rod connected to said piston and extending downwardly through said housing, said piston rod having its lower end connected to said latching assembly, said lower compartment being in pressure communication with said drilling fluid above said sealing support so that the pressure of said drilling fluid tends to drive said piston upwardly thereby applying a pulling force on said insert through said latching assembly.
 7. In a jet drilling assembly having a hollow bit body attachable to the bottom of a tubular drill string and a retrievable nozzle holder detachably mounted in said bit body, the improvement comprising a pulling apparatus adapted to be lowered through said drill string and including a hydraulic motor; a latching assembly depending from said hydraulic motor for attachment to said nozzle holder; and means for sealingly supporting said hydraulic motor in said drill string at an elevation above said nozzle holder, said latching assembly being upwardly movable responsive to actuation of said hydraulic motor, and said motor being actuably responsive to pressure above said support means.
 8. The invention as recited in claim 7 wherein said bit body has formed therein an internal opening including a generally axially extending portion and a diverging portion, said diverging portion being formed to receive said nozzle holder and sealingly support said nozzle holder in a fixed attitude, said opening being configurated to provide a seat for sealingly supporting said pulling device at an elevation above said nozzle holder, and said motor is a positive displacement piston hydraulic motor operatively responsive to the pressure internally of said bit above said seat.
 9. The invention as recited in claim 8 wherein said seat for supporting said pulling device extends circumferentially around said diverging portion and is configurated to support said pulling device in an attitude in which the direction of force applied to said nozzle holder is coincident to the direction of movement of said nozzle holder through said diverging portion.
 10. An apparatus for drilling wells, said apparatus comprising: a tubular drilling string; a drilling bit including a bit body connected to the bottom of said drilling string anD having a longitudinal opening formed therein, said opening being in registry with the internal opening in said drilling string whereby drilling fluid is conducted from the surface internally through said drilling string and said bit, a generally cylindrical nozzle holder passable internally through said drilling string and insertable into said body opening, said bit body being provided with a seat for fixedly and sealingly receiving said nozzle holder; a hydraulic motor passable internally through said drilling string and insertable into said bit body opening, said bit body being provided with a seat for sealingly receiving said hydraulic motor at an elevation above said nozzle holder; latching means depending from said hydraulic motor for attachment to said nozzle holder, said latching means being upwardly movable responsive to actuation of said hydraulic motor, said hydraulic motor being actuated by drilling fluid pressure above said hydraulic motor seat; and means for preventing actuation of said hydraulic motor until said hydraulic motor is positioned on said motor seat.
 11. The invention as recited in claim 10 wherein said hydraulic motor includes a support member having a shoulder for sealingly engaging said motor seat, a housing extending upwardly from said support member and having a cylindrical chamber formed therein, a piston reciprocably mounted in said chamber dividing said chamber into upper and lower compartments, and a piston rod extending downwardly through said support member and having its lower end connected to said latching means, said housing having a port intercommunicating said lower compartment and said bit body opening whereby the upward force developed by said hydraulic motor is proportional to the drilling fluid pressure in said drill bit opening.
 12. the invention as recited in claim 11 wherein the means for preventing actuation of said hydraulic motor includes a shear pin inserted in said rod and engageable with said support member thereby applying a holding force thereon, said shear pin being yieldable at a predetermined stress imparted thereon by said hydraulic motor.
 13. The invention as recited in claim 12 wherein said drilling bit is a hydraulic jet bit, said opening formed in said bit body including an upper straight portion axially aligned with the internal opening of said drill string and a lower diverging portion, said hydraulic motor seat being formed in said bit body in an upper portion of said diverging portion and said nozzle holder seat being formed in a lower portion of said diverging portion, said seats being arranged in axial alignment so that the direction of movement of said latching means and the direction of movement of said nozzle holder in unseating from said seat are in general alignment.
 14. The invention as recited in claim 13 wherein said bit body includes means for orienting the attitude at which said nozzle holder engages said nozzle holder seat. 